B-70 Valkyrie (Wallpaper 1) aircraft photo gallery | AirSkyBuster

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B-70 Valkyrie (Wallpaper 1)

Monday, October 24, 2011

B-70 Valkyrie, Bomber Supersonic Aircraft Wallpaper 1
image dimensions : 1092 x 682
B-70 Valkyrie (Wallpaper 1)
One . B-70 Valkyrie, Bomber Supersonic Aircraft. Photo, image, picture, wallpaper, review, specification.
The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep-penetration strategic bomber for the United States Air Force's (USAF) Strategic Air Command. Designed by North American Aviation in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly Mach 3+ at an altitude of 70,000 feet (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time. The introduction of effective high-altitude surface-to-air missiles (SAMs), the program's high development costs, and changes in the technological environment with the introduction of intercontinental ballistic missile (ICBM)s led to the cancellation of the B-70 program in 1961. Although the proposed fleet of operational B-70 bombers was canceled, two prototype aircraft were built as the XB-70A and used in supersonic test flights from 1964 to 1969. One prototype crashed following a midair collision in 1966; the other is on display at the National Museum of the United States Air Force in Ohio. As an offshoot of Boeing's MX-2145 manned boost-glide bomber project, the company partnered with RAND Corporation in January 1954 to explore what sort of aircraft would be needed to deliver the various nuclear weapons then under development. Providing for a long range and high payload were obvious requirements, but they also concluded that after bomb-release the plane would need supersonic speed to escape the weapon's critical blast-radius. An aircraft capable of carrying a reasonable bomb load to the Soviet Union from the continental United States had to carry a large fuel load (and thus be very large itself) due to the unrefueled range required. The aviation industry had been examining this problem for some time. There was considerable interest in the use of nuclear powered aircraft in the bomber role from the mid-1940s. This would allow the aircraft to have effectively unlimited range without requiring unlimited fuel loads. Another possibility was the use of boron-enriched "zip fuels", which improved the energy density of the fuel by about 40%,[6] and could be used in versions of existing engine designs. The U.S. Air Force followed these developments closely, and in October 1954 issued General Operational Requirement No. 38 for a new bomber with the intercontinental range of the B-52 and the Mach 2 top speed of the Convair B-58 Hustler. The new bomber was expected to enter service in 1963. The nuclear-powered bomber was placed under "Weapon System 125A" and pursued simultaneously with the chemical or zip fuel-powered bomber. The USAF Air Research and Development Command (ARDC) issued a new requirement for "Weapon System 110A", which asked for a chemical fuel bomber with Mach 0.9 cruising speed and "maximum possible" speed during a 1,000 nautical miles (1,609 km) entrance and exit from the target. The requirement also called for a 50,000 pounds (22,670 kg) payload and a combat radius of 4,000 nautical miles (4,600 mi, 7,400 km). The Air Force formed similar requirements for an WS-110L intercontinental reconnaissance system in 1955, but this was later canceled in 1958 due to better options. In July 1955 six contractors were selected to bid on WS-110A studies.[9] Boeing and North American Aviation (NAA) submitted proposals, and on 8 November 1955 were awarded contracts for Phase 1 development. In mid-1956, initial designs were presented by the two companies. Zip fuel was to be used in the afterburners to improve range by 10% to 15% over conventional fuel. Both designs featured huge wing tip fuel tanks that could be jettisoned when their fuel was depleted before a supersonic dash to the target. On both Boeing and North American designs, the entire outer portion of the wings was jettisoned with the fuel wing tanks. The two designs had takeoff weights of approximately 750,000 pounds (340,000 kg) with large fuel loads. The Air Force evaluated the designs, and in September 1956 deemed them too large and complicated for operations. The USAF ended Phase 1 development in October 1956 and instructed the two contractors to continue design studies. During the period that the original proposals were being studied, advances in supersonic flight were proceeding rapidly. The "long thin delta" was establishing itself as a preferred planform for supersonic flight, replacing earlier designs like the swept wing and compound sweep as seen on designs like the Lockheed F-104 Starfighter (and the earlier NAA design for WS-110). Engines able to cope with higher temperatures and widely varying inlet air speeds were also under design, allowing for sustained supersonic speeds. By March 1957, engine development and wind tunnel testing had progressed such that the potential for all-supersonic flight appeared feasible – the cruise-and-dash approach that had resulted in huge designs was no longer needed. The project decided that the aircraft would fly at speeds up to Mach 3 for the entire mission, instead of a combination of subsonic cruise and supersonic dash of the aircraft designs in the previous year. Zip fuel was to be burned in the engine's afterburner to increase range. Both North American and Boeing returned new designs with very long fuselages and large delta wings. They differed primarily in engine layout; the NAA design arranged its six engines in a semi-circular duct under the rear fuselage, while the Boeing design used separate podded engines located individually on pylons below the wing.

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